In the field of adaptive optics, an essential component is a mirror including a faceplate that is provided with a reflective surface region and is capable of being deformed in a controlled fashion at any particular time during the use of the deformable mirror to correct for or to introduce phase errors or perturbations in the wavefront of the light beam that impinges on and is being reflected from the reflective surface region of the faceplate, by selectively regionally changing the effective optical path lengths when and as needed. The configuration of the faceplate, and hence that of its reflective surface region, at any given time is determined by the action of one or more of typically a large number of actuator devices on the faceplate, and the counteraction of a restoration or spring mechanism of one kind or another. In each case, the respective actuator device exerts an action force on an affected zone or subaperture of the faceplate at least when activated to displace such zone out of its initial position, and the restoration mechanism urges the affected faceplate zone, either directly or via the actuator device, in the opposite direction. When the action force changes at any particular time, the affected faceplate zone is displaced out of its previous position with attendant concurrent change in the reaction force, such displacement continuing until the action and reaction forces are in equilibrium again, albeit at a different force magnitude level, in the newly acquired position of the affected zone.
In this context, it is highly desirable if not crucial to assure that the action and reaction forces act on the affected faceplate zone in a substantially coaxial fashion along the centerline of the subaperture that is substantially normal to the reflective surface, to avoid subjecting the faceplate to undesirable force moments resulting in unwanted faceplate stresses and/or distortions. This, however, is not easy to accomplish, especially because the available volume is limited, typically amounting only to a few cubic centimeters.
There are already known many different types of deformable mirrors and of actuator devices capable of providing the faceplate deflection, but they all possess limitations of varying nature. So, for instance, various types of actuators are presently being used in deformable mirrors equipped with metal faceplates that are commonly used in high power applications where the capability of the metallic materials to withstand and operate at relatively high temperatures, coupled with their relatively high thermal conductivity making it possible to cool the faceplate by circulating a coolant past the back face of the faceplate, are important if not decisive considerations. On the other hand, metal faceplates have certain disadvantages that directly affect the performance parameters of the various components and have particularly undesirable effects in relatively low power applications. The large mass, high coefficient of thermal expansion, only moderate surfaceability, long term dimensional instability and environmental susceptibility of metals are all known drawbacks encountered when using metallic faceplates.
Traditional glass mirror faceplates avoid a number of these problems, but the materials used therefor are of relatively low strength and/or brittle. These qualities make it very difficult if not impossible to use such faceplates with actuator devices that employ coil springs or diaphragm plates to urge the affected faceplate zones to their initial positions, mainly because of the relatively high tensile stresses that these mechanisms impose on the faceplate.
To avoid such problems, deformable mirrors using faceplates of conventional optical glasses have been built by employing a "sandwich" structure in which the actuator device itself constitutes a stressed link in the structural path of the reaction or restoration force. This structure, however, results in tensile loading of the actuators, which are typically made of ceramic materials possessing very little mechanical strength in tension. The result has been that delamination of multilayer actuators has become a chronic problem in such structures. Moreover, in such a structure, replacement of any actuator that may have been damaged or is in need of replacement for some other reason requires extensive refurbishment of the entire structural assembly of such deformable mirror.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a mirror actuator device which does not possess the disadvantages of the known devices of this kind.
Still another object of the present invention is to develop the actuator device of the type here under consideration in such a manner as to be particularly suited for use in a deformable mirror assembly.
It is yet another object of the present invention to devise a deformable mirror assembly utilizing a plurality of actuator devices of the above type, in which the actuator devices can be easily adjusted.
A concomitant object of the present invention is to design the deformable mirror assembly of the above kind in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.
A yet further object of the present invention is to construct the mirror assembly and the actuator device of the above kinds in such a manner as to minimize the amount of space occupied thereby and the number of parts employed therein.